The invention relates to the testing and measurement of the resistance to physical breakdown and formation of fine particles of manufactured solid adsorbent materials such as desiccant and catalyst pellets used in industrial dehydration processes.
Dehydration processes are used in many industrial applications and are particularly important for liquid and gas hydrocarbon dehydration in the oil and gas industry. Failure of adsorbent and catalyst beds due to physical breakdown of the adsorbent material after repeated regeneration cycles reduces the efficiency and cost effectiveness of the dehydration process in plant operations. Similarly, solid catalyst systems in refining processes can undergo physical breakdown during the process cycle.
This breakdown leads to the formation of fine particles of the solid material or xe2x80x9cfinesxe2x80x9d. The continued accumulation of fines results in an excessive pressure drop across the bed and eventually to the necessity for reduced throughput or premature replacement of adsorbent beds.
The current standard quality control test that measures the strength or hardness of molecular sieves, activated aluminas and catalysts pellets is the crush strength test. This crush strength test, in which a force is applied to the solid pellet (held between 2 plates) until the pellet breaks, is not adequate for assessing the potential of the material to resist breakdown into fines in industrial processes.
To date, manufacturers have not developed a standardized test procedure that measures the xe2x80x9cphysical stability or resistance to breakdownxe2x80x9d of an adsorbent material or catalyst in an industrial process. There is no test procedure that measures the ability of a desiccant to resist breakdown into fines when subjected to successive cycles of hot water or aqueous solutions and steam followed by regeneration or a drying cycle. No organization has provided the industry with a standardized test for evaluating this physical property. There is no test that can identify a material that will fail prematurely in service due to premature physical breakdown.
Some research into the effect of adsorption cycles on the physical properties of adsorbents has been undertaken using a column filled with the adsorbent material to be studied. A gas stream, containing a known amount of moisture, is passed through the column until saturation is achieved and this is followed by a drying cycle. Successive cycled of hydration and regeneration are then performed prior to the removal of the adsorbent for evaluation. The recovered adsorbent can then be evaluated by standard physical tests. Unfortunately such testing is very time-consuming and is unable to provide information on the potential of the adsorbent to break into fines during repeated regeneration cycles. No results from studies relating to the physical breakdown and/or resistance to fines formation after repeated regeneration cycles appear to have been published.
It is therefore one objective of this invention to provide an efficient and reliable method and apparatus for evaluating the physical stability of solid desiccant adsorbents when subjected to successive accelerated cycles of contact with hot aqueous solutions, and steam followed by rapid drying. The method of the invention can also be applied to evaluating the physical stability of other solid materials used as catalysts, e.g., refining catalysts.
An associated principal object is to provide a rating system based upon accelerated aging to reliably predict the relative useful life of solid adsorbents, catalyst supports and like manufactured articles subjected to cyclic wetting and drying processes during their service life.
Another object of the invention is to provide a method and apparatus for the accelerated aging of adsorbents of various shapes and sizes that provides relative physical stability information on the effect of size and shape of the particles in industrial service applications.
A further object of the invention is to provide an accelerated method and apparatus for determining the ability of the solid material to resist breakdown by contact with hot water or water-containing volatile component under conditions similar to those encountered in an industrial application. The test is designed to specifically evaluate the effect of water-soluble volatile components that are adsorbed with the water by the solid adsorbent during the dehydration process. Generally these volatile components, such as organic amines, are detrimental to the physical stability of the adsorbent.
It is also an object of the invention to provide an apparatus and method for improving the quality control that can also be utilized by the manufacturer of solid desiccant materials as an improved standard quality control test for production batches to provide data for grading each batch for purposes that can include warranting useful service life, replacement and maintenance schedules and product pricing.
Another object of the invention is to provide a means for establishing a quality control test for such materials to avoid production of sub-standard batches that would cause premature breakdown and excess fines formation when placed in operational service.
It is yet another object of the invention to provide a method and apparatus that can be used in evaluating the physical stability of solid catalysts, such as refining catalysts, that are subjected to process conditions that result in the eventual physical breakdown of the material. This breakdown reduces the effectiveness of the catalyst and adversely effects the efficient operation of the process.
As used herein, the term xe2x80x9cadsorbent materialxe2x80x9d means any commercially manufactured solid desiccant material that can be used for dehydrating process steams. Examples include molecular sieves, activated aluminas and silicas employed in dehydration applications. These materials come in a variety of shapes, including beads and extrudates, and a variety of sizes (0.5-10 mm). It is also to be understood that xe2x80x9cadsorbent materialxe2x80x9d includes any solid porous material, and particularly those that undergo exposure to heat and steam. This includes various shapes of manufactured articles, such as rings, branched cylinders, and the like which contain a catalyst, or which support a catalyst that are contacted by the process stream.
In its broadest aspect, the apparatus of the invention comprises a sample treatment chamber for containing a sample in a controlled environment that is isolated from ambient laboratory conditions. The treatment chamber is heated and has an associated cooling system for condensing water vapors withdrawn from the heated chamber. Also communicating with its interior are means for (a) the programmed delivery of a fluid to saturate the sample, which fluid can include water or an aqueous solution, and (b) subjecting the sample to a vacuum to expedite the drying process. After a predetermined number of wetting and dying cycles, the sample is evaluated for physical degradation. The sample material is sieved or screened and any degraded material, or fines, that pass through a sieve or screen of specific pre-determined mesh size is weighed. The ratio of the weight of any fines to the original sample weight is determined, and is preferably and conveniently expressed as a weight percent. A zero percent value for a predetermined number of cycles is optimum and confirms that no fines have been formed during the test protocol and that the material is likely to have a strong resistance to breakdown when subjected to process regeneration cycles.
The apparatus and method of the invention require a relatively small sample of a commercial solid adsorbent material in the form of discrete manufactured beads or extruded material that are subjected to repeated cycles in a laboratory-scale test apparatus under conditions that will lead to the accelerated degradation of the material. The process of the invention includes saturating the sample with water or an aqueous solution containing one or more additives and rapidly drying it under conditions of high temperature and vacuum. The relatively short cycle time allows statistically significant data to be collected within two to ten days. The apparatus is automated and is easy to construct and to program for operation. In a preferred embodiment, constructed for simultaneous comparative testing of several different product samples.
In one preferred embodiment, 60 cycles of 24 minutes/cycle, are completed using samples of about 25 grams. After each 60 cycles, the sample is screened and any fines are weighed and the percentage of fines based on the original dry weight of the sample is recorded. It has been found that it is desirable to complete at least 120 cycles in order to provide sufficient data. Preferably, up to 600 cycles are completed with fines measurement after each 60 cycles to obtain data for making comparisons between competing commercial products when a reliable assessment of the product(s) having the greatest potential service-life is needed.
The chamber is heated to a temperature in the range of from 118xc2x0 C. to 125xc2x0 C. and preferably maintained at a temperature of about 122xc2x0 C. A vacuum is preferably maintained to facilitate the drying and removal of water vapor. The water vapor is preferably condensed to facilitate the process.
The apparatus and method of the invention can be utilized to evaluate the ability of a material to resist breakdown after repeated cycles of exposure to environmental conditions similar to those encountered in industrial dehydration processes. The invention can be used by the industrial consumer of this material to identify the most suitable commercial material available.
The temperature, or temperature range, to which the test sample is subjected in the heated chamber does not necessarily closely replicate operating conditions in actual industrial dehydration processes. However, the higher temperature, or temperature range is similar to the conditions experienced by desiccant adsorbents during industrial regeneration processes. The preferred operating temperature, or temperature range has been determined to optimize the practice of the invention.
The water added to the sample is at ambient temperature. At the beginning of each of the cycles, the test sample is at about 122xc2x0 C., its temperature is reduced with the initial contact of the saturating water or aqueous solution, is gradually raised to the temperature at which the water or aqueous solution begins to evaporate and generate steam, following which the dried sample approaches or attains the maximum temperature of the heated chamber. Since a relatively small sample can be utilized in the method and the apparatus of the invention, a uniform or steady-state condition can be attained within the preferred cycle of 24 minutes. Thus, upon the addition of water at ambient temperature, the temperature of the test sample is lowered from, e.g., 122xc2x0 C., but the effects of the oven temperature and vacuum causes the water to be desorbed as steam, and the dry sample again reaches the stable interior temperature.
The particular size and/or shape of the material to be tested has not been found to have an effect on the practice of the invention. It is, of course, important to obtain representative samples of the commercial material to be tested. Sampling techniques for dry solids are well established in the art. This will be apparent to one of ordinary skill if each particle or piece of the material to be tested is relatively large, the number of pieces to be tested, and therefore the total starting weight of the sample may have to be adjusted accordingly to insure that a representative sample is subjected to the test.
From the description and example that follows, it will also be apparent that the invention can also be utilized by the manufacturer of materials subjected to repeated cycles of aqueous saturation and dehydration to establish an improved quality control standard for production batches and to provide a means for grading each batch for purposes that can include warrantying useful service life, replacement and maintenance schedules and product pricing.